Marriage is bullshit! My parents were married for 45 years then separated. In that time they had 5 kids and I wouldn't describe their union as happy, convenient, YES, but not HAPPY. Ironically both of their parents separated after the same amount of time. All those claiming to be happy now, you wait till 30 years, 35 years, 40 years then come back and tell me how happy you are. I don't think in my time I have ever met a happy couple, I have met plenty who try and fake it, but I am pretty good at seeing through bullshit!
The problem with humans is, they are 'MORE' creatures, they always want more, because they think what they want is better than what it is. When they finally get what they want, they realise the reality of it, that it wasn't as good as what they thought it was, and the only way to overcome that is too start the cycle again. Chasing an illusion. I think the best one can hope for is to be content with being in a miserable relationship. The alternative is to learn to live on your own, and be content with that.